This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. Section 119 from an application for METHOD FOR MAKING NETWORK DIRECT SYSTEM SELECTION IN A CELLULAR COMMUNICATION SYSTEM filed earlier in the Korean Industrial Property Office on May 13, 1999 and there duly assigned Serial No. 17146/1999.
1. Field of the Invention
The present invention relates to a cellular mobile communications system, and more particularly, a method for directly connecting a mobile station (MS) in communication with a mobile switching center (MSC) from one network to an MSC in another network.
2. Description of the Related Art
In a cellular mobile communication system, a service area is divided into a plurality of cells, each with a base station system (BS) therein. The base stations are controlled by a mobile switching center (MSC) to enable the MS to make voice or data communication while roaming from one cell to another. With reference to FIG. 1, there is illustrated a conventional cellular communications system, which includes a mobile station (MS) 10 in communication with a base station (BS) 20, and an MSC 30 coupled to a plurality of base stations, a PSTN Public Switched Telephone Network (PSTN) 60, and another MSC 40. The MSC coupled to the plurality of base stations (BSs) may be defined as one network.
The cellular network, as shown in FIG. 1, further includes a Home Location Register (HLR), which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information. The HLR 50 can service multiple MSCs, as shown in FIG. 1. A Visitor Location Register (VLR) 35 coupled to the MSC 30 is a database containing information about all MSs currently located within the MSC 30/VLR 35 area. Thus, the MSC establishes a call connection upon receiving a call request from the user of an MS, by accessing the HLR 50 and VLR 35/45 for the requisite identification information of the MSs registered in the network. If an MS 20 roams into a new MSC 40/VLR 45 area, the VLR 45 connected to the MSC 40 will request data about that MS 20 from the HLR 50 database. Accordingly, if the user of the MS 20 wishes to make a call, the local VLR 45 will have the requisite identification information. In the aforedescribed manner when the MS requests the call set-up or the location registration, the MS 30/40 first searches the VLR 35 or 45, then the HLR 50 retrieves various subscriber information of the MS.
In such mobile communications network, the HLR 50 can selectively elect one of the MSCs 30 and 40 to be connected to the MS, depending on the type of service requested by the MS. This is known as the Network Direct System Selection (NDSS), used to provide a specific service that is requested by the MS. For example, if an MS in communication with an MSC requests the Internet service but the MSC is not equipped with the packet data service capability, the HLR having the requisite information can determine another MSC with the Internet service capability to be connected to the MS. The operation of NDSS involves transmitting NDSS signaling messages and processing the message through the network (BS, MSC, HLR, VLR, etc.) which enables the MS to roam between different networks to receive various services or the optimal route. This type of NDSS operation is usually performed when the MS requests the registration of an additional function (e.g., voice message service, Internet service, call forwarding service, etc.), the location registration, or the call transmission.
The information regarding the current location of the MS is received in the CM SERVICE REQUEST message. Thus, when an MS in communication with the BS transmits the CM SERVICE REQUEST message with an NDSS code to request a certain feature/service, the VLR of the MSC relays this message to the HLR. The same message is relayed when the MS transmits the LOCATION UPDATE REQUEST message for registering the location of the MS, or when the MS transmits the CM SERVICE REQUEST message for requesting a call set-up as requested by the MS. Thereafter, the HLR confirms the NDSS code of the MS and determines the new MSC for providing the service as indicated in the NDSS code, then transmits the QUALIFICATION DIRECTIVE message or the REGISTRATION NOTIFICATION RETURN message back to the VLR of the MSC. Then, the MSC transmits the SERVICE RE-DIRECTION message to the MS via the BS to register the MS in the new MSC area or request the new MSC to generate a call. The address of the new MSC area is represented by the ID information included in the SERVICE RE-DIRECTION message.
However, in the above conventional NDSS operation, there are areas that need to be addressed to improve the communication efficiency. First, there is no means for the user of the MS to know whether the HLR has successfully registered the MS with a specific service as requested by the MS. For example, if the MS requests the Internet service or the voice mailing service, the user is not notified of whether the MS has been provided with the voice mailing service in the current the NDSS operation. Also, there is no protocol or set method for the VLR to transmit the QUALIFICATION DIRECTIVE message with the SERVICE RE-DIRECTION message therein from the HLR to the MS. Moreover, when performing the location registration through the NDSS operation, the procedures for transmitting the LOCATION UPDATE REQUEST from the MS to the MSC and for exchanging the REGISTRATION NOTIFICATION RETURN message between the MSC and the HLR are not defined by the TSB-80 of A-Interface in the present EIA/TIA North America CDMA Communications Standard. Furthermore, when the MS, which is already registered in the VLR, requires a call generation and transmits an NDSS code requesting a specific service, the VLR has no means to determine whether the MS is registered for the specific service. Hence, the VLR may establish a call-set up without consulting with the HLR and fails to provide the appropriate MSC that has the capability to provide the requested service.
It is an object of the present invention to provide a method for performing the Network Direct Select System (NDSS) in a communication system whenever the MS transmits an NDSS code requesting a specific feature/service from the system.
It is another object of the present invention to provide a method for performing the Network Direct Select System (NDSS) in a communication system whenever the MS executes the location registration.
It is a further object of the present invention to provide a method for performing the Network Direct Select System (NDSS) in a communication system whenever the MS attempts to establish a call set-up.
According to one embodiment of the present invention, a method for performing the NDSS operation of an MS in a cellular communications system includes steps of: inserting, by a BS, a dialed phone number with an NDSS code in a CM SERVICE REQUEST message to be transferred to a first MSC; transmitting, by the first MSC, an NDSS FEATURE REQUEST INVOKE message of the MS to the HLR after confirming the dialed phone number of the NDSS; transmitting, by the first MSC, a FEATURE REQUEST INVOKE CONFIRMATION message to the MS via the BS; upon receiving the FEATURE REQUEST INVOKE message from the first MSC, determining, by the HLR, whether a second MSC needs to be designated for providing the requested service; transmitting, by the HLR, a QUALIFICATION DIRECTIVE message to a first VLR of the first MSC and including a service re-direction information in the QUALIFICATION DIRECTIVE message if is determined to require the second MSC service; determining, by the first VLR, whether the QUALIFICATION DIRECTIVE message contains the service re-direction information; transmitting, by the first VLR, the service re-direction message including the service re-direction information and transmitting a command message to request the MS to report a connection failure to the second MSC; and, registering the location of the MS in a second VLR of the second MSC as directed by the service re-direction message.
According to another embodiment of the present invention, a method for performing the NDSS operation of an MS in a cellular communications system includes the steps of: transmitting, by the MS via a base station, a LOCATION REVISION REQUEST message including the return cause information of a previous NDSS operation failure to a first VLR of a first MSC; storing, by the first VLR, the information of LOCATION REVISION REQUEST message from the MS and transmitting a LOCATION REGISTRATION NOTIFICATION message including the return cause information to the HLR; revising, by the HLR, the location information of the MS and transmitting a LOCATION REGISTRATION NOTIFICATION RETURN message including service re-direction information after determining whether the LOCATION REGISTRATION NOTIFICATION message includes the return cause information and whether the MS requires the assignment of a new MSC; if the location REGISTRATION NOTIFICATION RETURN message includes the service re-direction information, transmitting, by the first VLR, a SERVICE RE-DIRECTION message including the service re-direction information and a command message to request the MS to report when the connection to the new MSC fails; and, registering the location of the MS in the second VLR of a second MSC as directed by the service re-direction message.
According to another embodiment of the present invention, a method for performing the NDSS operation of an MS in a cellular communications system includes the steps of: transmitting a CM SERVICE REQUEST message including a phone number dialed by the MS to a first MSC via a BS; searching, by the first MSC, the subscriber information of the MS from a first VLR; transmitting a LOCATION REGISTRATION NOTIFICATION message including the NDSS feature request invoke information of the MS from the first VLR to the HLR, if the subscriber information of the MS is stored in the VLR, or if the MS is registered with the NDSS code; transmitting a location REGISTRATION NOTIFICATION RETURN message including the subscriber information with service re-direction information from the HLR to the first VLR if the MS requires a new MSC; determining, by the first MSC, whether the subscriber information stored in the first VLR includes the service re-direction information; if the location REGISTRATION NOTIFICATION RETURN message includes the service re-direction information, transmitting a service re-direction message including the service re-direction information and a command message to request the MS to report if the connection to the new MSC fails; terminating the connection with the first MSC with the MS; and, initiating, by the MS, the generation of a call to a second MSC as directed by the service re-direction message.
As explain above, there are three embodiments utilizing the NDSS operation to perform a call set-up between the originating MSC and the terminating MSC. The first embodiment includes the event that the MS transmits a specific feature request; the second embodiment includes the event that the MS executes the location registration; and, the third embodiment includes the event that the MS originates a call. To this end, the HLR transmits the service re-direction information including the ID of the new MSC to the VLR of the originating MSC when the MS requires the NDSS operation. The originating MSC transmits a SERVICE RE-DIRECTION message including the service re-direction information to the MS so as to request the new MSC to execute the location registration or call generation.
According to the embodiment of the present invention, the CM SERVICE REQUEST message, transmitted from the base station to the MSC, for call generation and the LOCATION REVISION REQUEST message, transmitted from the MS for location registration, include the return cause information. The return cause information includes information relating to the failure cause of the previous service re-direction attempt. The return cause information, as set forth under the MAP interface of IS-735 standard, includes information indicating that the new MSC is not detected and that the MS does not support the NDSS operation. Accordingly, the MSC and the HLR may take proper action, such as re-attempting the call request, upon detecting the failure of the MS for the NDSS via the return cause information from the MS.
In the embodiment, in order to receive the return cause information from the MS, the MSC includes a parameter for commanding the MS to report the cause of the NDSS failure to the new network in the service re-direction message that is transferred to the MS. Thereafter, the MS includes the return cause information in the CM SERVICE REQUEST message or the location revision request message that is transferred to the MSC so that the MSC can transfer the return cause information to the HLR.
In the embodiment of the present invention, the subscriber information of the MS further includes the information indicating whether it is registered or activated for the NDSS. Thus, upon detecting the subscriber information of the MS requesting a call generation which is also activated for the NDSS, the VLR requests the subscriber information from the HLR to determine whether the MS requires a new assignment of the MSC. Thus, the present invention provides the methods for checking the NDSS of the MS by the HLR in three embodiments.
The foregoing and other objects, features, and advantages of the invention will be apparent from the following, more detailed description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, the emphasis instead placed upon illustrating the principles of the invention.